1. Field of the Invention
The present invention relates to a cleaning device for removing toner remaining on an image carrier after transferring a toner image formed on the image carrier by applying electrophotography, and to an image forming apparatus, such as a printer, a copying apparatus or a facsimile apparatus, to which this cleaning device is applied.
2. Description of the Related Art
Conventionally, in an image forming apparatus such as an electrophotographic copying machine or a printer, an image is generally formed by the following series of processes: a charging process for uniformly charging, for example, an electrophotographic photosensitive drum; a latent image forming process for forming an electrostatic latent image on the photosensitive drum; a developing process for developing the electrostatic latent image by using toner; a transferring process for transferring the toner image obtained by the developing process to a transfer material; a fixing process for fixing the transferred toner image to the transfer material; and a cleaning process for clearing away the remaining toner, etc. adhering to the photosensitive drum after the transfer in order to make the apparatus ready for the next image forming process. The toner remaining after the transfer, generated in the photosensitive drum cleaning process, has conventionally been all recovered in a toner container in the cleaner.
As a result of the recent demand in the market for a reduction in the running cost of image forming apparatuses, contrivances for increasing the service life of the parts of the apparatus have been examined and put into practical use. An example thereof is a so-called toner supply type image forming apparatus, in which a consumed portion of toner is repeatedly supplied to the developing device, thereby making it possible for the developing device to be used for a long period of time. FIG. 10 shows an example of this conventional toner supply type image forming apparatus.
As shown in FIG. 10, the image forming apparatus has a rotary drum type electrophotographic photosensitive member, i.e., a photosensitive drum 1. The photosensitive drum 1 is rotated clockwise (in the direction of an arrow A), and a bias is applied to a charging roller 2 by a power source 2a, whereby the photosensitive drum 1 is uniformly charged. A laser beam 3 from an exposure means is applied to this photosensitive drum 1, whereby image information is formed on the surface of the photosensitive drum 1 as an electrostatic latent image.
As the photosensitive drum 1 rotates, the latent image reaches a developing section opposed to a developing device 4, and is developed by using toner carried by a developing sleeve 4b of the developing device 4. During the development, a bias is applied to the developing sleeve 4b by a power source 4a. In order that the toner layer on the developing sleeve 4b for use in development may have a fixed uniform thickness, the developing sleeve 4b is in elastic contact with a doctor blade 6. This blade 6 is formed of urethane rubber or the like, and its base section is mounted to a container 4c of the developing device 4. When toner 5 in the developing container 4c has been consumed as a result of development and become less than a predetermined amount, the user opens a supply inlet 7 in the upper section of the container 4c to supply new toner.
As the photosensitive drum 1 rotates, the toner image formed on the photosensitive drum 1 by the development of the latent image is conveyed to a transfer section opposed to a transfer roller 8, and transferred to a transfer material 9, which is supplied to the transfer section from a paper feed section (not shown) with a predetermined timing. The transfer material 9 which has passed the transfer section 9 is separated from the photosensitive drum and conveyed to a fuser (not shown), where the fixing of the toner image on this transfer material is effected.
The portion of toner 100 (including other adhering matter such as paper powder) remaining on the photosensitive drum 1 after the transfer process is cleared away by being scraped off the drum by a cleaning blade 110 constituting cleaning means, and is accommodated in a cleaner container 120 as toner 101.
In the above construction, the photosensitive drum 1, the transfer roller 2, the developing device 5, and the cleaning means including the cleaning blade 110, the cleaner container 120, etc. are, as shown in FIG. 10, integrally supported by supporting means and assembled as a process cartridge, and this cartridge can be detachably mounted to the apparatus body.
However, in the above-described toner supply type image forming apparatus, the amount of toner 101 recovered in the cleaner container 120 increases as toner is supplied to the apparatus, with the result that the size of the cleaner container has to be rather large.
In order that the size of the entire apparatus may be reduced, it is desirable that the size of the cleaner container 120 be reduced. For that purpose, it is necessary to frequently perform maintenance operations such as the replacement of the cleaner container to dispose of the recovered toner. There is a method for achieving, apart from the reduction in the size of the cleaner container 120, an improvement in the efficiency in the use of toner, according to which the recovered toner is mechanically fed to the developer container 4c, which, however, involves a complicated structure.
It is an object of the present invention to solve the above problem in the prior art. The present invention aims to reduce the amount of toner recovered by the cleaning means.
Another object of the present invention is to make the capacity of the toner container of the cleaning means as small as possible.
Still another object of the present invention is to make the capacity of the toner container of the cleaning means as small as possible and to reduce the volume of the process cartridge including this cleaning means.
A further object of the present invention is to provide an image forming apparatus having such cleaning means.
To achieve the above objects, the present invention provides a cleaning device for removing a remaining portion of toner remaining on an image carrier after toner on the image carrier which carries a toner image has been transferred to another material, the cleaning device comprising: a conductive brush roller to which a bias voltage of a polarity that is the same as the proper polarity of toner is applied in order to remove that portion of the residual toner on the image carrier after the image transfer process whose polarity has become opposite to the proper polarity of toner used for development; a roller electrode which comes into contact with the brush roller and to which a bias that is of a polarity opposite to that of the brush roller to electrostatically attract the toner adhering to the conductive brush; and scraping means for scraping off the toner adhering to this roller electrode, wherein that portion of the residual toner existing on the image carrier after the image transfer process whose polarity has become opposite to the proper polarity of toner is removed by the brush roller and that portion of the residual toner which maintains the proper polarity is allowed to pass.
Further, the present invention, which achieves the above objects, provides an image forming apparatus to which the above-described cleaning device is applied.